Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative illness characterized by a progressive and relatively selective loss of motoneurons. The overall goal of this laboratory is to understand the mechanisms of selective motoneuron degeneration in ALS, and to devise effective approaches to halt the processes leading to cell death in this disorder. The central hypothesis under investigation is that increases in intracellular calcium act as early triggering events in the process leading to motoneuron destruction, and that mechanisms of regulating intracellular calcium play critical roles in determining the selective vulnerability of neurons to injury. The motoneuron cell line VSC4.1, developed in this laboratory by fusion of mouse N18TG2 neuroblastoma cells with embryonic rat ventral spinal cord cells, expresses biochemical and morphological features characteristic of motoneurons when differentiated in cAMP and aphidocolin. VSC4.1 cells also express neuronal voltage-gated calcium currents which can be enhanced by immunoglobulins from ALS (but not disease control) patient sera. These ALS immunoglobulins also increase intracellular calcium, and initiate calcium-dependent cell death, in VSC4.1 cells. However, the parental cell line (N18TG2) is resistant to ALS immunoglobulin-induced toxicity, and exhibits lower levels of calcium current expression as well as higher levels of immunoreactivity for the calcium-binding proteins calbindin-D28K and parvalbumin. Quantitative comparison of the effects of ALS immunoglobulins in these two cell lines thus provides an excellent model for determining the relative roles of differentiation state, calcium channel expression, and mechanisms of intracellular calcium regulation in determining susceptibility to calcium-dependent cytotoxicity induced by ALS immunoglobulins. Further studies will extend the results of these in vitro studies in cell lines to adult rat motoneurons in slice preparations, using electrophysiologic, optical, and immunohistochemical techniques to characterize motoneurons from nuclei known to be susceptible or resistant to cell loss in ALS. These experiments are expected to provide further insight into the mechanisms underlying selective vulnerability in ALS, and to suggest potential therapeutic strategies aimed at increasing neuronal resistance to injury in ALS and other neurodegenerative disorders. The proposed studies will be carried out at the facilities of Baylor College of Medicine, under the sponsorship of Dr. Stanley Appel, who has a long-standing interest in ALS and other neurodegenerative diseases.